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Eberspacher D5W ECU Constant Overheat Error

Eberspacher ECU 25 1599 50 00 00
Eberspacher ECU 25 1599 50 00 00

Here’s another Eberspacher control unit, this time from an ancient D5W 5kW water heater. The system in this case is just flaky – sometimes the heater will start without fault & run perfectly, then suddenly will stop working entirely.
The error codes are read on these very old units via an indicator lamp connected to a test terminal. In this case the code was the one for Overheat Shutdown.

Considering this fault occurs when the heater is stone cold, I figured it was either a fault with the sensor itself or the ECU.

Temperature Sensor
Temperature Sensor

The temperature sensor is located on the heat exchanger, right next to the hot water outlet fitting. I’m not sure what the spec is, but it reads exactly 1KΩ at room temperature.

ECU PCB
ECU PCB

The PCB is held into the aluminium can by means of crimps around the edge that lock into the plastic terminal cover. Inserting a screwdriver & expanding the crimps allows the PCB to be slid out.

Casing Crimps
Casing Crimps

The factory date stamp on the microcontroller dates this unit to March 1989 – considerably older than I expected!
Unlike the newer versions that use transistors, this ECU has a bunch of PCB relays to do the high current switching of the water pump motor, fan motor & glowplug.
Overall the board looks to be solidly constructed, with silicone around all the larger components.

ECU PCB Solder Side
ECU PCB Solder Side

Here’s the solder side of the PCB, which has a generous coating of sealant to keep moisture out.

Bad Joint Closeup
Bad Joint Closeup

Looking at the solder joints for the row of relays on the top side of the PCB, it looks like that there’s some dry joints here.
I suspect that years of vibration has taken it’s toll, as the relays are otherwise unsupported. It wouldn’t be possible to use silicone to secure these devices as they are completely open – any sealant would likely stop them from operating.

Resoldered Joints
Resoldered Joints

Using a very hot soldering iron I managed to get the joints to reflow properly, using lots of flux to make sure the conformal coating didn’t interfere with the reflow.

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Boating: Drydock Time – The Inspection

Drydock
Drydock

It’s that time again, so the boat is out of the water for it’s 3-yearly maintenance. Some things over the past few months have been bugging me, namely a pronounced vibration in the running gear while underway. (Issue was easy to spot here!).

10-Ton Jack
10-Ton Jack

nb Tanya Louise being a very odd vessel, she has quite a significant keel, so once the dock was drained, some manual jacking was required to get her level on the blocks. Without this extra work there is such a pronounced heel that it’s impossible to do anything on board.

Chocks
Chocks

On the opposite side, wooded blocks are placed for the bottom of the hull to rest against. Jacking up a 58-ft 25-ton boat by hand onto some timbers was nerve-wracking to say the very least!

The bottom of the hull has already been jet-washed to remove 3-year’s worth of slime, weed growth & the old blacking. First job is to get a fresh coat of paint on.

Running Gear
Running Gear

Looking under the hull shows the reason for the high level of vibration – the prop shaft has actually *worn through* the bearing & stern tube, to the extent that there’s not much left of the assembly! The only thing holding the shaft in place at this stage is the stuffing box inside the boat & the shaft coupling to the hydraulic motor.
, stern tube,
A replacement standard-issue Cutless bearing will be fitted, after the remains of the old tube are cut back to make room. To facilitate mounting the bearing, a custom stainless P bracket is being made at a local engineers, for me to weld onto the bottom of the hull.

(Surprised we didn’t lose the shaft, lucky that I kept pestering to get her out of the water!).

More to come as work progresses!

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Mini USB Soldering Iron

USB Soldering Iron
USB Soldering Iron

Here’s a novel little gadget, a USB powered soldering iron. The heating tip on these is very small & might be useful for very small SMD work. Bigger joints not so much, as it’s only rated at 8W. (Still breaks the USB standard of 2.5W from a single port).

These irons aren’t actually too bad to use, as long as the limitations in power are respected. Since nearly everything has a USB power port these days, it could make for a handy emergency soldering iron.

Heater Socket
Heater Socket

The heater & soldering bit are a single unit, not designed to be replaced separately. (I’ve not managed to find replacement elements, but at £3 for the entire iron, it would be pretty pointless).
Above is the socket where the heater plugs in, safely isolating the plastic body from any stray heat.

DC Input Jack
DC Input Jack

The DC input is a 3.5mm audio jack, a non-standard USB to 3.5mm jack cable is supplied. Such non-standard cables have the potential to damage equipment that isn’t expecting to see 5v on an audio input if it’s used incorrectly.

Touch Sensor & LED
Touch Sensor & LED

There isn’t actually a switch on this unit for power management, but a clever arrangement of a touch button & vibration switch. The vertical spring in the photo above makes contact with a steel ball bearing pressed into the plastic housing, forming the touch contact.

MOSFET
MOSFET

The large MOSFET here is switching the main heater current, the silver cylinder in front is the vibration switch, connected in parallel with the touch button.

PCB
PCB

The main controller is very simple. It’s a 555 timer configured in monostable mode. Below is a schematic showing the basic circuit.

555 Monostable
555 Monostable

Big Clive also did a teardown & review of this iron. Head over to YouTube to watch.